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Anchor Escrow

Introduction

This Solana program is an escrow — it lets a user swap a specific amount of one token for a desired amount of another token.

For example: Alice offers 10 USDC and wants 100 WIF in return.

Without an escrow, users would have to swap tokens manually and trust each other. The escrow program acts as a trusted third party that only releases tokens to both sides when the swap can complete atomically. Neither party can take the other's tokens and run.

Alice and Bob transact directly with each other through the program, so there's no spread or middleman fee taken on the swap.

Usage

Run the tests with pnpm test (as configured in Anchor.toml).

Credit

Based on Dean Little's Anchor Escrow, with a few changes to make it easier to discuss in class.

Changes from the original

One challenge when teaching is avoiding ambiguity — names have to be clear and not confused with anything else.

  • Several custom handler functions were replaced by helpers from @solana-developers/helpers to reduce file size.
  • Shared token-transfer logic now lives in instructions/shared.rs.
  • The upstream project uses a custom file layout. This version uses the 'multiple files' Anchor layout.
  • Contexts are separate data structures from the functions that use them. There's no need for OO-style impl patterns here — no mutable state is stored in the context, and the methods don't mutate it.
  • The name 'deposit' was overloaded. deposit is both a verb and a noun, which made the code hard to read:
    • deposit #1 → token_a_offered_amount
    • deposit #2 (in make()) → send_offered_tokens_to_vault
    • deposit #3 (in take()) → send_wanted_tokens_to_maker
  • seed was renamed to id, because it conflicted with the seeds used for PDA derivation.
  • Escrow was used for both the program name and the account that records an offer. People kept confusing the offer account with the vault.
    • Escrow (the program) → still Escrow.
    • Escrow (the offer) → Offer.
  • receive was renamed to token_b_wanted_amount, since receive is a verb and not a good name for an integer.
  • mint_a → token_mint_a (what the maker offered and what the taker wants).
  • mint_b → token_mint_b (what the maker wants and what the taker must offer).
  • makerAtaA → makerTokenAccountA
  • makerAtaB → makerTokenAccountB
  • takerAtaA → takerTokenAccountA
  • takerAtaB → takerTokenAccountB